Age is recorded in years based on participant self-report or medical records at the time of enrollment in the study. Data will be reported as mean, median, and range.

Frailty is measured using the Clinical Frailty Scale (CFS), a clinician-reported tool that assesses a patient's vulnerability to adverse health outcomes based on their physical and cognitive condition. The scale ranges from 1 to 9, where 1 indicates very fit and 9 indicates terminally ill. Higher scores reflect greater frailty.

Resilience is measured using the Brief Resilience Scale (BRS), a patient-reported questionnaire designed to assess the ability to recover from stress. The scale ranges from 1 to 5, with higher scores indicating greater resilience.

Optimism is measured using the Life Orientation Test-Revised (LOT-R), a patient-reported questionnaire that assesses an individual's general tendency toward optimism versus pessimism. Scores range from 0 to 24, with higher scores indicating greater optimism.

This outcome measures how well patients cope with side effects from cancer treatment, operationalized as the self-reported impact of symptoms on various quality of life (QoL) domains. Symptoms are identified using disease-specific EORTC questionnaires. The impact of these symptoms is measured using items from the EORTC QLQ-C30 Core Quality of Life questionnaire, supplemented with additional questions covering domains not fully captured by the QLQ-C30, including physical functioning, emotional well-being, independence, social relationships, meaning in life, and daily activities. Scores are aggregated by calculating mean scores per domain and overall, with higher scores indicating greater impact and therefore lower coping effectiveness.

Shared decision-making is measured using the 5-Likert scale, 17-item I-Share questionnaire, a patient-reported outcome measure that assesses the patient's experience of shared decision-making during medical consultations. Higher scores indicate a greater perceived level of shared decision-making.

Decisional conflict is measured using the Decisional Conflict Scale, a patient-reported questionnaire that evaluates uncertainty and perceived difficulty in making a health-related decision. Scores range from 0 to 100, with higher scores indicating greater decisional conflict. 16 item 5 response categories.

Decision regret is measured using the Decision Regret Scale, a patient-reported questionnaire that assesses the level of regret a patient feels after making a health-related decision. Scores range from 0 to 100, with higher scores indicating greater decision regret. 5 items, 5 answer categories

The Modified Control Preference Scale is a patient-reported measure that assesses the patient's perceived and preferred role in the treatment decision-making process. Responses are categorized into three groups reflecting whether the patient prefers a passive role (decision made by the clinician), a shared role (decision made together with the clinician), or an active role (decision made primarily by the patient). 1-Item, 5 categories.

This outcome records the type of companion (e.g., partner, child, friend, or other caregiver) who was present during the treatment decision consultation. Information is extracted from the electronic medical record (EMR), where the presence and relationship of companions are noted by clinical staff when available. Data will be reported as counts per companion type.

Shared decision-making is measured through researcher-coded audio recordings of clinical consultations, using the 4SDM observational framework. The coding assesses the extent to which shared decision-making principles were applied during the consultation, including steps such as team talk, option talk, preference talk, and decision talk.

Patient-centeredness is measured using a patient-reported questionnaire that assesses the extent to which patients perceive their care as aligned with their individual values, needs, and preferences. Scores indicate the degree of patient-centeredness experienced, with higher scores reflecting a greater perception of personalized, respectful, and responsive care.

Sex is recorded as part of routine clinical documentation and extracted from the electronic medical record (EMR). Categories include: male and female. Data will be reported as the number of participants in each category.

Migration background is determined based on self-reported data on the participant's own country of birth and the countries of birth of both parents. Participants are categorized according to national guidelines into groups such as: no migration background, first-generation migrant (participant born abroad), or second-generation migrant (participant born in the reporting country with at least one parent born abroad). Data will be reported as counts per category.

Education level is measured based on self-reported data from participants indicating the highest level of education they have completed. Categories include, for example: primary education, secondary education, vocational training, and higher education (e.g., university or equivalent). Data will be reported as the number of participants in each education category.

Living situation is measured using self-reported data from participants, indicating with whom they live. Response categories include: living alone, living with a partner, living with family (e.g., children or parents), or living with others (e.g., housemates, caregivers). Data will be reported as the number of participants in each category.

Health literacy is measured using a three-item Dutch version of the Set of Brief Screening Questions (SBS-Q), a patient-reported questionnaire that assesses an individual's ability to understand and use health-related information. Each item is scored on a 5-point Likert scale. Responses are combined into an overall score, with higher scores indicating lower health literacy. Data will be reported as mean scores and/or categorized into levels of health literacy (e.g., adequate vs. inadequate).

Description: Functional independence in basic activities of daily living is assessed using the Katz ADL Index, a patient-reported measure. The Katz ADL evaluates the ability to perform tasks such as bathing, dressing, toileting, transferring, continence, and feeding.

Scoring: The Katz ADL provides scores ranging from 0 (completely dependent) to 6 (completely independent), with higher scores indicating greater independence.

This outcome captures which multidisciplinary tumour working group (e.g., breast, lung, gastrointestinal) was responsible for managing each case. The data are extracted from the medical record or tumour board documentation. Each participant is assigned to a tumour working group based on their primary diagnosis. Data will be reported as the number of participants per tumour group.

The tumor type is classified based on histological or pathological examination results documented in the medical record. Tumors are categorized according to established classification systems relevant to the cancer type (e.g., adenocarcinoma, squamous cell carcinoma). Data will be reported as counts per tumor type category.

The overall stage of the cancer is determined according to the TNM classification system, based on tumor size (T), lymph node involvement (N), and presence of metastases (M). Stages are categorized from I to IV, with higher stages indicating more advanced disease. Data will be reported as the number of participants in each stage category.

The TNM score summarizes cancer staging by evaluating three components: T (tumor size and extent), N (lymph node involvement), and M (presence of distant metastases). Each component is assessed according to standard clinical criteria. The combined TNM score is used to classify disease severity and guide treatment decisions. Data will be reported as individual T, N, and M categories and as overall stage groups.

The hospital where the patient receives care is recorded in the electronic medical record (EMR). This information provides context regarding the healthcare setting and available infrastructure. Data will be reported as counts of patients per hospital.

The number and types of clinicians involved in each patient's care are extracted from the electronic medical record (EMR). This includes consultations and interactions with various specialists such as oncologists, surgeons, radiologists, palliative care specialists, and others. Data will be reported as the total number of clinicians seen per patient and as a breakdown by clinician specialty.

This outcome captures details of the specific clinical consultation during which the primary treatment decision was made, as documented in the EMR. Data include the date of the consultation and the context/type of decision discussed, such as surgery, chemotherapy, or palliative care. This identifies the critical discussion shaping the patient's care plan.

The primary clinician responsible for managing the patient's care is identified based on documentation in the EMR. This includes the clinician's name, medical specialty (e.g., oncologist, surgeon), and their role in coordinating treatment and decision-making for the patient.

Appropriateness measures the extent to which the IODM intervention aligns with clinical needs, goals of healthcare professionals, and existing oncological care pathway guidelines. It reflects how well the intervention fits within the clinical context. Data are collected via a questionnaire completed by healthcare professionals using a standardized assessment tool.

Acceptability refers to the extent to which healthcare professionals perceive the IODM intervention as satisfactory and suitable for use in oncological care. This includes their overall perception of its value and usefulness in clinical practice. Data are collected via the Acceptability of Intervention Measure (AIM) questionnaire completed by healthcare professionals.